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Full text of "The Cathach, Deposited in the Museum"

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370 

April 24. 
SIR WILLIAM BETHAM, in the Chair. 

The Chairman informed the Academy, that Sir Richard 
O'Donnell had consented to deposit the Cathach, containing 
a MS. of the Psalms in Latin, by St. Colombkill, in the Mu- 
seum of the Royal Irish Academy. 

Resolved, — That the marked thanks of the Academy be 
returned U\ Sir Richard O'Donnell for his kindness. 



Read, a letter from the Rev. T. R. Robinson, accom- 
panying a box containing an original Pyrometer of Wedge- 
wood, presented to the Academy by Miss Edgeworth, 
(H. M.R.I. A.) 

" Dear Mac Cullagh, 

" Our friend, Miss Edgeworth, has requested me 
to present from her to the Academy a Wedgewood's Pyro- 
meter, which, as unfortunately I cannot attend this evening, 
I commit to your care. This instrument is remarkable, as 
being the first attempt to place within reach of the manu- 
facturer and the chemist an easy method of measuring, at 
least approximatively, the temperature of their furnaces. It 
consists, as is well known, of a pair of converging bars, which 
measure, by a graduation on them, the contraction of clay 
cylinders that have been heated ; this remains permanent, 
and were it, as Mr. Wedgewood supposed, a function of 
temperature alone, would suffice for all practical purposes. 
Many circumstances, however, have interfered with its gene- 
ral employment. The set of clay pieces which were used in 
the first instance were made of natural clay found in Corn- 
wall. By these the numbers given in treatises of chemistry 
for the fusing points of the more refractory metals were de- 
termined, and I think it probable that Mr. Kirwan used them 
in his researches ; Sir James Hall, I think, did not. Mr. 



371 

Wedgewood had stated in his memoir that the supply of the 
clay was inexhaustible; but when the stock first made was 
disposed of, he was unable to find the identical spot where 
it had been obtained, and the contraction of the new speci- 
men was different. Had he used it as he did the other, and 
merely directed the employment of a number by which to 
multiply the indications of the scale, no inconvenience would 
have resulted ; but he thought he might bring it to an iden- 
tity by adding ' earth of alum,' obtained by precipitating 
alum by carbonate of potassa; a product which Apjohn or 
Kane will tell you is very far indeed from being pure alumina. 
This unhappily made the contraction irregular, and the clay 
pieces much less capable of resisting a high heat. Its indi- 
cations were found to differ from those of the first set, and 
it fell into disuse, especially for two reasons. The first that 
Wedgewood had assigned to his degrees, a value enormously 
too large, so that he supposed the extreme heat of a furnace 
to be about 30000 of Fahrenheit, when it is Only 4000. 
Many years since, in our Transactions, I had pointed out 
this error, and corrected it, with tolerable success, as was 
long afterwards confirmed by Daniell and Prinsep. The se- 
cond, that a long exposure to a low heat produces the same 
contraction as a short exposure to a high. This is said by 
Sir James Hall to have been established by Dr. Kennedy, 
whose experiments, however, are no where published ; and 
I confess that I doubt the fact. Guy ton De Morveau has 
even made an observation which may account for the mistake. 
He found that similar pieces exposed for half an hour in a 
powerful furnace, one surrounded by siliceous sand, the 
other by powdered charcoal, marked 90 and 60, in conse- 
quence of the different conducting powers of these media. 
Now it is possible that the Scotch philosopher may have 
overlooked this influence, and not allowed time enough for 
the higher temperature to be fully transmitted. The py- 
rometers of Daniell and others which have since been con- 

VOL. II. I 



372 

trived, are so much more cumbrous and elaborate than this, 
that I hope it may yet be revived; and if so, the chemists, 
who may construct pieces for themselves, would find it useful 
to compare them with Wedgewood's old standard. A single 
cylinder is sufficient for this, as after measuring a compara- 
tively low temperature, it will still contract when submitted 
to a higher. This I know to have been one of the original 
and genuine set presented to the late Mr. Edgeworth by its 
inventor, and therefore, independent of its probable utility, 
precious as a relic of two such men, and still more so as the 
gift of our illustrious countrywoman to a body, of whose 
scientific triumphs she is proud, and in whose welfare I know 
her to be deeply interested. 

" T. R. Robinson. 
" April 24, 1843." 

Resolved, — That the letter be referred to Council, for 
special notice and attention. 



H. Smith, Esq. exhibited an ancient dress, found in a 
bog at a considerable depth, near the Abbey of Kilkenny. 



A number of interesting antiquities, found at Ballyrowan, 
in the Queen's County, by Mr. Harrison, were presented by 
the Rev. B. I. Clarke, to the Academy. 

The thanks of the Academy were presented to Mr. Clarke 
for his donation. 



Sir Wm.Betham made a communication on the antiquity 
of certain languages. 



DONATIONS. 

Astronomical Observations made with Ramsden's Zenith 
Sector, and Catalogue of the Stars which have been observed 
at the different stations of the Ordnance Survey in England